Wire-bonding is a common method used for interconnecting integrated circuits and electronic devices to leads. A typical apparatus and method for forming wire bonds between contacts or bond pads on integrated circuit dies and dies of electronic devices, and corresponding leads is illustrated in U.S. Pat. No. 4,600,138. As disclosed in the U.S. patent, a bond head is shown moving from a first bonding location to a second bonding location. An end of a wire is bonded to the first bonding location by the bond head. The bond head moves vertically away from the first bonding location to draw a length of wire necessary to make a wire bond. The bond head is then moved to the second bonding location with subsequent bonding of the wire to the second bonding location. The bond head is then used to pull and subsequently break away the remaining wire from the second bonding location. Thereafter, the bond head is ready to be moved to another first bonding location for effecting another wire bond.
Typically, the bond head is heated to assist the formation of the wire bond. The heat and subsequent pressure applied by the bond head fuse the end of the wire to the contact or bond pad. Ultrasonic vibration in conjunction with a heated bond head may also be used to effect a wire bond. Typically, a single bond head is used for making all of the wire bonds of the integrated circuits and electronic devices. As should be recognized by those skilled in the art, such an operation is inherently mechanical in nature and thus disadvantageously limits the speed with which interconnections can be made.
In addition to the disadvantage of the speed limitation of the sequential process of wire bonding, there is another disadvantage associated with wire bonding especially when used in the manufacturing of a light-emitting diode (LED) to bond the LED die to a lead.
Typically in the manufacturing process of an LED, the connection of a die to a lead is provided by threading a wire through a standard wire bonding capillary in a bond head and heating the end of the wire to form a ball. The ball is applied to a bond pad on the die and is bonded to the bond pad. The capillary is then moved to a lead with the wire being threaded through the capillary until the wire has reached the lead. The wire is then stitch bonded to the lead. In making the connection, the wire is looped above the bond pad at the neck to minimize stress on the wire. Despite such care to reduce stress at the neck and the stitch, the likelihood of damage to the wire, such as cracking during the rigorous conditions of surface-mounting-technology (SMT) soldering and during usage is high. As temperature changes during such processes, the die and the encapsulant expand and contract at different rates. These different expansion rates stress the neck and the stitch of the wire bond mechanically. These stresses are high especially when the LED is operated at elevated temperatures of more than 150 degree Celsius. To curb such temperature excursions during LED operation, the amount of current drawn by the LED has to be limited.
Another disadvantage associated with wire bonding in the manufacturing of tiny SMT LEDs is the difficulty in achieving fine pitch bonding due to the relatively large size of the bond head.
The foregoing therefore creates the need for a method for making faster and more reliable interconnection than what can be achieved with wire bonding. In the manufacturing of an LED, there is also a need to provide a stronger and more robust interconnection between a die to a lead.